The present invention relates to perpendicular recording heads for use with magnetic recording media. More specifically, the invention relates to heads having layers of low moment, non-magnetic and high moment materials within the main write pole to minimize the problem of magnetic remanence during transitions of the pole.
Perpendicular recording heads for use with magnetic recording media typically include a pair of magnetically coupled poles, consisting of a main write pole having a small bottom surface area, and an opposing pole having a large bottom surface area. A coil is located adjacent to the main write pole, for inducing a magnetic field within the pole. A typical magnetic recording medium for use with such a recording head includes a recording layer having a plurality of magnetically permeable tracks, with each track divided into sectors. The tracks are separated by nonmagnetized transitions. A magnetically permeable lower layer, which is magnetically soft relative to the tracks, is located below the recording layer.
An important advantage of perpendicular recording is its ability to generate significantly stronger magnetic fields than longitudinal systems. Strong magnetic recording fields permit the use of high anisotropy magnetic recording media, thereby limiting superparamagnetic instabilities at high recording densities.
In some prior art embodiments of perpendicular recording heads, the opposing pole of the perpendicular write pole of the recording head can also form one of two substantially identical shields for the read elements, which are parallel to the trackwidth. The read element is located between these shields. Typical read elements include magneto-resistive (MR), giant magneto-resistive (GMR), spin valves, and tunnel magneto-resistive (TMR). A pair of electrical leads are located on opposing sides of the read elements to provide a sense current to the read elements.
The recording head is separated from the magnetic recording medium by a distance known as the flying height. The magnetic recording medium is moved past the recording head so that the recording head follows the tracks of the magnetic flux within the main write pole, causing the magnetic fields in the tracks to align with the magnetic flux of the main write pole. Changing the direction of electric current in the coil changes the direction of the flux created by the recording head, and therefore changes the magnetic fields within the magnetic recording medium. A binary xe2x80x9c0xe2x80x9d is recorded by maintaining a constant direction of magnetic flux through the main pole, and a binary xe2x80x9c1xe2x80x9d is recorded by changing the direction of magnetic flux through the main pole.
To read from the magnetic recording medium, the read element is separated from the magnetic recording medium by the flying height. The magnetic recording medium is moved past the read element so that the read element follows the tracks of the magnetic recording medium. As the magnetic recording medium passes under the read element, the magnetic fields within the recording medium orient the adjacent magnetic fields within the ferromagnetic read element layers so that they are either parallel (corresponding to minimum resistance) or anti-parallel (corresponding to maximum resistance), depending on the direction of the magnetic field being read from the recording medium. A sense current is passed through the read element by a pair of electrical contacts, thereby enabling the resistance of the read element to be detected. A constant level of resistance, whether the minimum resistance or the maximum resistance, is read as a binary xe2x80x9c0xe2x80x9d. A changing level of resistance, regardless of whether the change is from minimum to maximum resistance or maximum to minimum resistance, is read as a binary xe2x80x9c1xe2x80x9d.
FIG. 4 illustrates prior art write pole 64. The prior art main write pole 66 is typically made from a single material having a uniform magnetic moment. It is generally desirable to provide a sufficiently thick main write pole 66 to provide a sufficient channel for the magnetic flux for a strong magnetic field. As used herein, the thickness, designated by the arrow B, refers to the dimension of the main pole 66 that is substantially parallel to the track, and the main pole""s width, designated by arrow C in FIG. 6, refers to the dimension of the main pole 66 parallel to the trackwidth. Typically, main pole 66 of composed of a material having a high saturation magnetic moment (M), thereby resulting in a strong magnetic write field. A strong magnetic write field permits use of a magnetic storage medium 16 having a high anisotropy, thereby limiting superparamagnetic instabilities at high recording densities.
The typical prior art write pole shown in FIG. 4 is limited by several difficulties. First, prior art write poles lack the ability to generate very localized magnetic recording fields at their trailing edge, which are important for minimizing the track width necessary to accommodate the skew angle. Further, presently available write poles exhibit magnetic remanence during transition of the write pole.
The geometry of the write pole is significant in the magnetic remanence problem. It is known that when the lateral dimensions of the pole tip become smaller than the height of the pole tip or when the dimensions of the pole tip become comparable to the domain wall thickness, the magnetization remanence of the recording tip becomes a significant factor in the performance of the write pole. A non-zero remanence causes non-linear head response, which leads to a number of technical difficulties, including data self-erasure, and non-linear transition shift.
The magnetic remanence problem is shown graphically in FIG. 1. FIG. 1(a) shows an ideal graph of magnetic field (H) generated by application of a current through the coil versus magnetization of the write pole. Ideally, as the field increases either positively or negatively, the magnetization of the write pole increases until it reaches saturation magnetization (MS). It is at or near this state that the write pole actually writes data onto the disc (usually the head during writing is slightly under-saturated). As the current is removed from the coil, the magnetization should ideally return to zero, as shown in FIG. 1(a). However, often the actual behavior of the write pole can be as shown in FIG. 1(b). As the field decreases, the magnetization of the write pole stays at or near the saturation point, instead of returning to zero, creating a hysteresis effect. To make the magnetization of the pole return to zero requires the application of a magnetic field in the opposite direction field. This problem can cause unwanted data to be written to the disc.
The magnetic remanence problem can usually be avoided by careful control of the magnetic domain structure within the pole tip. Unfortunately, this approach does not work when the geometry of the pole tip is such that the entire pole tip comprises a single magnetic domain.
Therefore, it would be desirable to have a write pole which is able to generate a strong magnetic recording field at the trailing edge of the write pole while minimizing the problem of magnetic remanence during transition of the pole.
The present invention is embodied as a perpendicular recording head having a main write pole consisting of a thin layer of material having a high magnetic moment which forms the trailing edge thereof, a layer of non-magnetic de-coupling material adjacent the trailing edge, and the remainder of the write pole and the opposing pole are composed of a material having a low magnetic moment.
The main body of the write pole of the recording head is made from material having a low magnetic moment. However, in drive designs where skew angle sensitivity is not a problem, a high-moment magnetic material can be used. A layer of de-coupling non-magnetic material is placed adjacent the main body portion. A trailing edge portion made from material having a high magnetic moment is placed adjacent the non-magnetic material opposite the main body portion. This structure provides the advantages of localizing a strong magnetic field in the region defined by the thickness of the high moment material at the write pole""s trailing edge while at the same time minimizing the effects of magnetic remanence. The trailing edge portion and the main body portion are antiferromagnetically coupled via magneto-static or exchange interaction to minimize the total energy of the system. In drive designs where skew angle is a problem, the main body portion can be composed of a magnetic material having a low magnetic moment to minimize the problem.
The strong magnetic fields provided by this write pole structure permits the use of a magnetic recording media having a high anisotropy, thereby limiting super paramagnetic instabilities at high recording densities. Additionally, the highly localized magnetic field permits the use of a narrower trackwidth while avoiding problems created by the skew angle, because the trackwidth is required only to accommodate a small portion of the write pole instead of the entire write pole.
One embodiment of the present invention includes a recording head combining a read portion and a write portion. The write portion is generally of perpendicular configuration. A typical perpendicular recording head includes a main pole, an opposing pole magnetically coupled to the main pole, and an electrically conductive coil adjacent to the main pole. It is desirable that the flux be concentrated as it flows into or eui out of the main write pole and dispersed as is flows into or out of the opposing pole, to avoid having both poles write on the disc. Therefore, the air-bearing surface (bottom) of the opposing pole will typically have a surface area greatly exceeding the area of the air-bearing surface of the main write pole. Electrical current flowing through the coil creates a flux through the main write pole. The direction of the flux may be reversed by reversing the direction of current flow through the coil.